1. Field of the Invention
This invention relates to leachate collection systems used in landfills.
2. Description of the Prior Art
A relatively new method for constructing landfills so as to minimize the potential for contamination of the surrounding environment is through use of a leachate containment and collection system. Following excavation of the landfill, an impermeable membrane, often referred to as a geomembrane, is placed in the hole. Good practice stipulates, however, that in addition to containment of the landfill, the leachate, or liquid that drains from the waste, must be collected. This is accomplished by placing a geonet over the geomembrane. As the leachate drains from the landfill, it collects in the geonet and flows to central collection points where is can be pumped to the surface either for treatment or recirculation. If left exposed, the geonet would become clogged in a very short period of time by solids from the landfill. To prevent this, a layer referred to as the geotextile is placed over the geonet. The geotextile can be either a woven or non-woven polypropylene, polyester, or polyethylene mat. There are many variations possible, including multiple layers of geomembranes, nets, textiles, gravel beds and drain pipes. The leachate flow should be maintained over the life of the landfill, which can be 30 years or longer. If the leachate flow falls below a specified volume, the system is generally regarded as clogged and, at great expense, the clogged system must be excavated, unclogged, and replaced.
A significant cause of clogging in leachate collection systems is due to the growth of microorganisms in and on the geotextiles and geonets. This condition is described in detail in a paper by G. R. Koerner and R. M. Koerner entitled "Biological Clogging in Leachate Collection Systems," which appeared in the proceeding of a Seminar on the Durability and Aging of Geosynthetics, Drexel University, Dec. 8-9, 1988. Others have suggested that an antimicrobial agent be impregnated into the plastic making up the geotextile or geonet. However, that method is insufficient to exert a significant, long lived, antimicrobial effect on the geonet or geotextile, resulting in undesirable biological fouling and shortening the useful life of the landfill.